1. Field of the Invention
The invention relates to an alarm system and method for a vehicle that gives an alarm to a driver by changing the acceleration of a host vehicle in order to avoid a collision between the host vehicle and an obstacle and to minimize damage that will be caused by such a collision.
2. Description of the Related Art
For example, in Japanese Patent Application Publication No. 9-286313 (JP-A-9-286313), there is an apparatus that prevents impact of a vehicle which includes obstacle detecting means for detecting an obstacle, a warning means for warning the driver by decelerating the vehicle according to the detection by the obstacle detecting means, and a vehicle speed detecting means. The apparatus warns the driver by decelerating the vehicle more when the vehicle speed detected by the speed detecting means is high. Also, for example in Japanese Patent Application Publication No. 2005-31967 (JP-A-2005-31967), there is a warning apparatus for a vehicle gives an impact to a driver by applying a braking force to a host vehicle if it is determined that there is a high probability of collision based on the relative distance and relative speed between the host vehicle and an obstacle, which are input in the host vehicle, thereby giving an alarm to the driver in order to avoid a collision between the host vehicle and the obstacle. If it is determined that there is a high probability of collision, such an apparatus for a vehicle applies a braking force to the host vehicle so that the acceleration of the host vehicle is equal to the target acceleration which is a fixed negative value.
The apparatuses for a vehicle described above apply a braking force to the host vehicle so that the acceleration of the host vehicle is equal to the target acceleration which is a fixed negative value. Accordingly, the amount of change in the acceleration vary depending on the acceleration of the host vehicle that is achieved before issuance of an alarm. As a result, various inconveniences are caused. For example, if a braking force is applied to the host vehicle so that the preset negative acceleration is achieved while the host vehicle is accelerating, the driver may feel a sense of discomfort in the operation of the host vehicle because the difference in the acceleration between before and after issuance of an alarm is excessively large. On the other hand, if a braking force is applied to the host vehicle so that the preset negative uniform acceleration is generated while the host vehicle is decelerating, only a small effect may be produced by the braking operation for giving an alarm to the driver, because the difference in the acceleration between before and after issuance of the alarm is excessively small.